1. Field of the Invention
The present invention relates to an apparatus for diverting gas hydrates away from a subsea connector attached to a subsea wellhead. More particularly, the present invention provides a gas hydrate diverter adapted to be installed over a subsea wellhead using a remotely operated vehicle for the purpose of diverting gas hydrates away from a subsea connector attached to the wellhead.
2. Description of Relevant Art
Hydrates of hydrocarbon gases have long presented serious problems in the drilling of oil and gas wells, particularly in polar drilling and in wells drilled under very deep water in temperate or equatorial regions. Gas hydrates, also referred to as gas clathrates, are crystalline solid structures made up of an ice-like mixture of gas and water. In particular, the gas molecules are trapped within a cage of water molecules. Natural gas hydrates may contain a wide range of gas molecules including hydrocarbons, most commonly methane, as well as other gases such as nitrogen, oxygen, carbon dioxide, hydrogen sulfide, and inert gases. Due to cold temperatures and high pressures, these naturally occurring gas hydrates are trapped beneath the ocean floor in a frozen state. However during deep water drilling of hydrate-containing strata, the hydrate-containing strata surrounding a hole (i.e., borehole) being drilled is heated due to heat generated from the rotation of the drilling bit as well as from pumping surface temperature drilling fluids down the out the drill bit and through the drill pipe. The heat generated during the drilling process heats the surrounding hydrate-containing strata around the drill pipe, or conductor pipe, to a temperature above freezing which causes melting of the frozen hydrates and release of the gas hydrates in the liquid and gas phases which are then free to migrate up and through the ocean floor. The released gas hydrates in liquid and gas phases tend to migrate up via a path of least resistance and typically travel along the exterior of the drill pipe or conductor pipe due to the micro-fractures formed in the strata adjacent the pipe during drilling. After the gas hydrates travel along the exterior of the pipe and exit the ocean floor, the gas hydrates continue to migrate upwardly through the sea water near a conductor housing (or conductor pipe) protruding above the ocean floor, then pass a subsea wellhead positioned above the conductor housing, and then the migrating gas hydrates tend to collect and become trapped inside a subsea connector attached to an upper portion of the subsea wellhead. At cold ocean floor temperatures the gas hydrates freeze again while trapped within the subsea connector that is designed to be removably attached by latching mechanisms within the connector to an upper portion of the subsea wellhead. When the gas hydrates freeze while trapped within the subsea connector, the subsea connector gets frozen or stuck to the wellhead as the connector or connector latches cannot be shifted or unlatched due to the presence of the frozen gas hydrates trapped inside the connector.
To remove a subsea connector frozen to a subsea wellhead, typically a subsea remotely operated vehicle (ROV) is deployed from the drilling rig to perform the task of heating the connector by pumping warm water or ethanol on the connector for hours in order to get the frozen gas hydrates to thaw enough to unlatch the connector from the wellhead. This process is extremely time consuming and costly as it can take hours to days to get a connector to unlock. In addition, a frozen connector presents a dangerous condition for a drilling rig to be attached to the wellhead, via the frozen connector, without being able to disconnect from the wellhead at a moments notice. Such dangerous situations may arise for example during a storm, loss of dynamic positioning, or during an underwater blowout when a drilling rig can not move off location in an emergency situation because the drilling rig is effectively latched to the ocean floor due to the rig being tethered to the connector which is frozen to the subsea wellhead.
Currently a heavy metal hydrate diverter attached to the exterior of the conductor housing is used to deflect gas hydrates away from the subsea connector located above a subsea wellhead which is positioned atop the conductor housing. One problem with a conventional metal hydrate diverter is that the metal hydrate diverter does not effectively provide an adequate seal around the conductor housing that prevents gas hydrates from collecting at the subsea connector. Another disadvantage of the conventional metal hydrate diverter is that it is very heavy weighing in excess of 1000 pounds (e.g., 1400 lbs.) which requires the heavy metal diverter to be installed onto the conductor housing at the surface rendering the drilling rig idle for about an hour while this operation is completed. This requirement means that expensive rig time (e.g., $12,000 per hour) must be devoted to the installation of the heavy metal hydrate diverter onto the conductor housing and the subsequent placement of the conductor housing onto the ocean floor.
Thus an objective of the present invention is to provide a gas hydrate diverter that effectively diverts gas hydrates away from the subsea connector in order to prevent collection of these hydrates at the connector which subsequently freeze and render the connector unreleasably connected to a subsea wellhead. Another objective of the present invention is to provide gas hydrate diverter that can be installed subsea without requiring the use of a drilling rig. There is a great economic incentive to allow the drilling rig to carry on with other tasks while another means such as an ROV is used to deploy and install a gas hydrate diverter that effectively diverts gas hydrates away from the subsea connector.